Recently, studies of optical materials are being made actively, and in particular, in the field of lens materials, it is much desired to develop materials excellent in high refractivity, low dispersion (high Abbe's number), heat resistance, transparency, easy shapability, lightweightness, chemical resistance, solvent resistance, etc.
As compared with inorganic materials such as glass, plastic lenses are lightweight and hardly crack, and can be shaped into various forms; and therefore, not only for spectacles but also recently for other optical materials such as mobile camera lenses or pickup lenses, plastic lenses are rapidly growing popular. Regarding the starting material for producing high-refractivity plastic lenses, polycarbonate is known as one typical example for them. Recently, however, it is desired to further increase the refractivity of the lenses for thinning them; however, polycarbonate could not fully satisfy the requirement.
Accordingly, it has become desired to develop a resin material more excellent than polycarbonate and to increase the refractivity of the material itself for producing thin lenses. For example, a technique of introducing a sulfur atom into a polymer (e.g., JP-A 2002-131502, 10-298287), and a technique of introducing a halogen atom or an aromatic ring into a polymer (e.g., JP-A 2004-244444) have been studied actively. In addition, a technique of using a resin with a 2-mercaptobenzothiazole structure or a 2-mercaptobenzoxazole structure introduced into the side chain of a polymer via a phenylene group has been developed (JP-A 2-29401).
On the other hand, it is known that, when a resin with a 2-benzothiazole group or a 2-benzoxazole group directly bonding to the main-chain structure of a polymer is used as an organic EL device material, then the device enables bright emission and has good durability (JP-A 2000-87027). However, the patent reference says nothing relating to the refractivity and the coloring resistance of the resin, and the usefulness of the material for optical parts is still unknown.
Although the above proposals have been made to attain higher refractivity of resins, a plastic material having high refractivity and good transparency and capable of being a substitute for glass has not as yet been developed. For optical fibers or optical waveguides, materials differing in refractivity may be combined or a material having refractivity distribution may be used. For these, therefore, it is desired to develop a technique of controlling the refractivity of plastics in any desired manner.
It is difficult to increase the refractivity of organic substances alone; and therefore, a method for producing a high-refractivity material is reported, which comprises dispersing a high-refractivity inorganic substance in a resin matrix (e.g., JP-A 2003-73559). For retarding the transmitted light attenuation owing to Rayleigh scattering, it is desirable to uniformly disperse inorganic fine particles having a particle size of at most 15 nm in a resin matrix. However, primary particles having a particle size of at most 15 nm tend to aggregate extremely easily, and therefore it is extremely difficult to uniformly disperse the particles in a resin material. In addition, in consideration of the transmitted light attenuation in the optical path length corresponding to the thickness of a lens, the amount of the inorganic fine particles to be added must be limited. Accordingly, it has heretofore been impossible to disperse fine particles in a resin matrix at a high concentration, not lowering the transparency of the resin.
Further reported are a shaped article of a resin composition, which comprises mainly a thermoplastic resin composition with ultra-fine particles having a number-average particle size of from 0.5 to 50 nm dispersed therein, and of which the mean birefringence per mm of the optical path length is at most 10 nm (e.g., JP-A 2003-147090); and a thermoplastic material composition comprising a thermoplastic resin having a refractive index and an Abbe's number expressed by specific numerical formulae, and inorganic fine particles having a specific mean particle diameter and a specific refractive index, and an optical part comprising the composition (e.g., JP-A 2003-73563, JP-A 2003-73564, JP-T 2004-524396). These comprise inorganic fine particles dispersed in a resin, but could not exhibit sufficient properties from the viewpoint of dispersing the fine particles in a resin matrix at a high concentration without lowering the transparency of the resin.
On the other hand, regarding an organic-inorganic hybrid composition, for example, reported is a method of melt-kneading inorganic particles organic-modified on their surfaces, and an acid group-having resin, in which, however, the amount of the inorganic particles added is about 1% by mass or so and is not enough (JP-A 2004-217714). Also reported is an organic-inorganic composite composition in which the surface-modifying group of inorganic particles is bonded to a resin via a linker (JP-A 2004-352975); however, this is problematic in that the bonding formation requires high-temperature operation, and in addition, the composition may gel and therefore could not exhibit sufficient properties from the viewpoint of the shaping workability thereof. Anyhow, these references say nothing relating to thick transparent shaped articles usable for high-refractivity lenses.
Plastic lenses produced by the use of the resins described in the above-mentioned JP-A 2002-131502, 10-298287, 2004-244444 and 2-29401 are excellent in that they have a higher refractivity than conventional lenses. However, the lenses are problematic in that the heat resistance of the resins is low and the resins color in thermal shaping; and therefore, they have problems in their production methods and in the products themselves. Specifically, a material composition which satisfies high refractivity, heat resistance, transparency and lightweightness and of which the refractivity can be controlled in any desired manner, and an optical part comprising the composition are not as yet found out, and it is desired to develop them.